JP3614713B2 - Date and time identification method and GPS receiver - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a GPS (Global Positioning System) that measures the position of a GPS receiver on the ground based on a positioning signal transmitted from a GPS satellite orbiting the earth, and more particularly to a WN (Week) in a GPS receiver. Number) relates to the handling of information.
[0002]
[Prior art]
GPS is a positioning system comprising a predetermined number of GPS satellites in orbit around the earth, a GPS receiver mounted on a mobile object on the ground or carried by humans and animals, and ground control equipment for controlling the GPS satellites. It is. The GPS receiver selects more than the required number of GPS satellites in a position that can be seen from the current position, receives positioning signals from the selected GPS satellites, and performs a predetermined positioning calculation based on the received positioning signals, thereby And the moving speed is obtained and provided to the user, for example, the operator of the mounted moving body.
[0003]
More specifically, the positioning signal transmitted from the GPS satellite includes information indicating the general orbit of the GPS satellite group, information indicating the detailed orbit of the source GPS satellite, time information indicating the transmission time of the positioning signal, and the like. It is out. The GPS receiver receives a positioning signal including these pieces of information while obtaining the receiving time of the positioning signal. From the difference between the time when the GPS satellite transmits the positioning signal and the time when the GPS satellite receives the positioning signal. The distance to the GPS satellite is obtained. This distance is called a pseudorange because it includes a clock error in the GPS receiver. The GPS receiver generally selects a predetermined number or more of GPS satellites in accordance with a predetermined rule from a plurality of GPS satellites in a position that can be seen from the current position based on the orbit information and the current time of the GPS satellites. Find the pseudorange of. On the other hand, the positioning signal includes the outline and detailed orbit information of each GPS satellite. In the GPS receiver, when orbit information and pseudoranges are obtained for more than the required number of GPS satellites, the position of the satellite is selected by using the obtained orbit information while calculating its own position by geometric calculation. I do. Also, the user's own moving speed is obtained by a technique such as Doppler shift detection.
[0004]
The time information transmitted from the GPS satellite includes WN information and Z count. The WN information is information that is incremented each time the week changes and is reset to an initial value, that is, 0 when the week starting on January 6, 1980 is the 0th week. In the current specification, since the WN information is 10 bits, the upper limit value of the WN information is 2 ¹⁰ −1 = 1023. In addition, the Z count is information that indicates a scale of a clock that makes one turn in one week. In the GPS receiver, the current week is specified using the WN information, and the time is specified by specifying the day of the week and the time using the Z count.
[0005]
[Problems to be solved by the invention]
However, the WN information is reset to the initial value when the upper limit value is reached as described above. Since the week starting on January 6, 1980 is the 0th week, the week starting on August 22, 1998 corresponds to the 1024th week. Accordingly, the WN information is reset to the initial value 0 on August 22, 1998, and the week starting on that day is newly set as the 0th week. That is, with a period of about 19.7 years, WN information circulates in the range of 0 to 1023, which is its value range.
[0006]
This process becomes a problem when the GPS receiver is used for a long period of time exceeding 19.7 years. As an example, assume that a GPS receiver was manufactured on January 4, 1998. The week to which this day belongs is the week of WN = 939, that is, the 939th week for GPS. This GPS receiver will reach August 22, 1999, in the second year since it was manufactured. At this point, the WN information is reset. The misconception of the week at this point is, for example, that information or determination logic indicating that “WN = 0 is a week starting from August 22, 1999” is incorporated in the GPS receiver in advance at the time of manufacture. Can be avoided. However, that is also until August 2017, when about 19.7 years have passed since manufacture. When the WN information becomes a value indicating week 939 again, that is, when the GPS receiver is in the 1024th week, the GPS receiver starts the current week on January 4, 1998. I misunderstand that it is a week.
[0007]
However, even when such a situation is reached, there is almost no problem in deriving the pseudorange because the Z count may be used for deriving. Rather, the weekly misrecognition of GPS receivers associated with the circulation of WN information appears in the form of difficulty in acquiring positioning satellites and increased burden on the connected device.
[0008]
First, it is assumed that the week derived in the GPS receiver based on the positioning signal received from the GPS satellite is a week that differs from the true week by the circulation period of WN information (about 19.7 years) × natural number. It is also assumed that the clock in the GPS receiver keeps the correct time including the week. In this case, the transmission time derived from the WN information, that is, the transmission time in which the week is incorrect, and the reception time measured by the clock in the GPS receiver, that is, the week is correct, are large corresponding to the week recognition error. Since a time difference occurs, the GPS receiver calibrates its internal clock based on the time derived from the WN information, that is, the wrong time. After performing this processing, the GPS receiver selects a predetermined number of GPS satellites that are currently visible based on the orbit information collected before that time and the time obtained from the built-in clock, and selects the selected GPS satellites. Try to capture the signal from. However, the position of the GPS satellite in the orbit changes depending on the orbit of the GPS satellite and the rotation of the earth. Specifically, since the orbiting period of the GPS satellite is about 11 hours and 58 minutes and the rotation period of the earth is about 24 hours, the position of a specific GPS satellite viewed from any point on the earth is 1 day. It shifts by about 4 minutes in between. If this difference of about 4 minutes is accumulated over 19.7 years, it will be 4 hours and 50 minutes. Therefore, if a GPS satellite is calibrated using an incorrect time derived from WN information as a reference and a GPS satellite is selected using the time obtained from the clock, the GPS satellite may be captured by chance. The signal cannot be captured and positioning cannot be performed. In order to avoid this state, conventionally, processing such as recollecting the trajectory information by a procedure such as cold start fixing has been unavoidable. However, even in that case, the date / time information obtained based on the WN information remains in error.
[0009]
The weekly misrecognition of the GPS receiver accompanying the circulation of the WN information also affects the device on the side that uses the output of the GPS receiver in the form of imposing a hardware or software burden. Since the GPS receiver is a positioning device that is relatively small and has high positioning accuracy, it is generally often used in combination with a car navigation device, a portable information terminal, a personal computer, or the like. In this type of device, information such as a position and a moving speed obtained from a GPS receiver is generally displayed in characters, displayed superimposed on a map, or output by voice. At that time, the current date and time are often displayed and output as audio. At that time, if the date and time display and audio output can be performed based on the time obtained by the GPS receiver, the circuit configuration of the car navigation device or the like should be simplified or the software processing should be reduced. It is. However, in consideration of the phenomenon that the date output is greatly mistaken when the WN information circulates, it is better to avoid that the car navigation device or the like receives the date / time information from the GPS receiver and uses it for the output.
[0010]
The present invention has been made to solve such a problem, and an object thereof is to realize a GPS receiver capable of accurately recognizing the current week even after WN information circulates. .
[0011]
[Means for Solving the Problems]
In order to achieve such an object, the date and time specifying method according to the present invention includes: (1) WN information that is incremented each time a week changes and is reset to an initial value when a predetermined upper limit value is reached; A step of receiving a Z count giving a time at a GPS signal from a GPS satellite as part of a positioning signal, (2) a step of detecting the number of times the WN information has circulated in the range from a predetermined point in the past to the present, and (3) And a step of specifying a transmission time of the positioning signal based on the obtained week and the received Z count.
[0012]
For example , WN information received from a GPS satellite is stored in a car navigation map information storage medium as a part of the reception history, and the number of laps of WN information from a predetermined point in the past to the present is calculated based on the stored reception history. Step of calculating, or receiving leap second information indicating a cumulative error occurring in the GPS system clock from a predetermined past time to the present from the GPS satellite, and WN from the past predetermined time to the present based on the received leap second information The number of laps is detected by one of the steps of calculating the number of laps of information. As a reference example, a step of manually setting the number of laps of WN information from a predetermined time in the past to the present, and a step of receiving the number of laps of WN information from a predetermined time in the past to the present from the outside can be cited.
[0013]
In this way, the WN information generates information about how many times it has circulated from a predetermined point in the past (for example, when WN = 0, such as January 6, 1980, or when the GPS receiver is manufactured or used). However, by using this, it is possible to continue to obtain accurate week information from the GPS receiver, and thus the date and time information derived based on the information, over a period of about 19.7 years. As a result, it is not necessary to re-receive the positioning signal, and the circuit configuration of the connection destination device, for example, the car navigation device is simplified, and the processing burden is reduced.
[0014]
In particular, the example in which the number of laps is detected by manual setting can be implemented with a slight circuit change of the GPS receiver. Examples of receiving the number of laps from the outside are provided for periodic / irregular reception of the number of laps via a communication line, reception of broadcast waves in which information indicating the number of laps is multiplexed, connection destination devices such as car navigation devices It can be realized easily by reading from a map database, etc., and in some cases, it can be implemented without adding hardware. In the example of deriving the number of laps from the reception history, it is only necessary to use the internal memory of the GPS receiver or a partial storage space of various external storage media, so no additional hardware is required and simple implementation is possible. is there. An example of using leap second information is to effectively use leap second information that has been transmitted from GPS satellites in the past, and can be implemented with only slight changes or additions to the time derivation procedure in the GPS receiver. Implementation is easy because no additional wear is required and resources in the GPS receiver are not consumed.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the member which is common between embodiment, and the overlapping description is abbreviate | omitted.
[0016]
FIG. 1 shows a configuration of a GPS receiver according to an embodiment of the present invention. In the figure, the reception control calculation unit 10 is timed by a preset position or a position obtained by the previous positioning, orbit information collected by the navigation data demodulation unit 14 so far, and a clock 12. Based on the current time, combinations of a predetermined number or more of GPS satellites to be captured are determined and set in the receiver 16. The receiving unit 16 receives a positioning signal from a GPS satellite belonging to the combination set by the reception control calculation unit 10 using the antenna 18 and outputs information such as a synchronization timing and a synchronization phase. The pseudorange measurement unit 20 derives a pseudorange to the GPS satellite that is the transmission source of the positioning signal based on the information and the Z count, and outputs the pseudorange to the position calculation unit 22. The navigation data demodulator 14 demodulates navigation data including time information, orbit information, and the like from the received signal from the receiver 16 and supplies the demodulated navigation data to the reception control calculator 10 and the position calculator 22.
[0017]
The position calculation unit 22 obtains the current position, speed, and the like based on the output of the pseudo distance measurement unit 20 and the output of the navigation data demodulation unit 14, and supplies the current position, speed, and the like to a navigation device (not shown). The position calculation unit 22 also determines the current week based on the WN information among the time information supplied from the navigation data demodulation unit 14, determines the day of the week and time based on the Z count, and the date and time obtained as a result thereof. Is supplied to a navigation device (not shown). The position calculation unit 22 compares the date and time obtained in this way with the time measured by the clock 12, and when there is a difference that cannot be ignored between the two, the position calculation unit 22 obtains the time based on the WN information and the Z count. The timepiece 12 is calibrated with reference to the time.
[0018]
A characteristic constituent member in the present embodiment is a circulation number detection unit 24 that gives information indicating the number of circulations of WN information to the position calculation unit 22. In GPS, WN information, which is information giving a total week with the week starting from January 6, 1980 as the 0th week, is transmitted from each GPS satellite as part of the time information in the positioning signal. . Since the WN information is 10 bits, as shown in FIG. 2A, the value range of 0 to 1023 is circulated with a period of about 19.7 years. In this embodiment, the number of laps detected by the lap number detecting unit 24 and supplied as information to the position calculating unit 22 is the number of laps at which the WN information is counted from a predetermined point in the past, for example, January 6, 1980, at the present time. It is a value indicating whether or not there is. In the example of FIG. 2C, the number of laps is counted with reference to January 6, 1980. The first round is counted as the first round, the next round is counted as the second round, and so on.
[0019]
The principle of detecting the number of laps in the lap number detector 24 can be broadly divided into the following four types. The first detection principle is to detect the number of laps from a setting operation by the user. As a typical example, as shown in FIG. 3A, a hardware switch 24a for manually setting the number of laps is provided in the GPS receiver, and the state of this switch 24a is transferred to the position calculation unit 22. There is a form of reading. In addition, since the GPS receiver and its connection destination device are provided with various switches for the operation by the user, if possible, any one of these switches may be used as the switch 24a.
[0020]
The second detection principle is to receive information about the number of laps from the outside. As a typical example, as shown in FIG. 3B, a receiving unit 24c and a demodulating unit 24d that receive a terrestrial radio signal using the antenna 24b and demodulate information on the number of laps are provided. 3), a receiving unit 24c and a demodulating unit 24d for receiving and demodulating information on the number of laps via a wired or wireless network 26 are provided, or in the external storage medium 28 as shown in FIG. There is a form in which the written information is read by the drive device 30 and information related to the number of laps is read into the position calculation unit 22 via the interface 24e.
[0021]
Among these, since the forms shown in FIGS. 3B and 3C are forms using communication, they can be combined with a DGPS (Differential GPS) function. Conventionally, DGPS employs a system configuration that transmits positioning error correction information and position information before and after correction via wireless, the Internet, etc., so that information related to the number of laps is transmitted in addition to such information. In this case, the present invention can be implemented in the form shown in FIG. 3B or 3C without adding any special device. Moreover, the form shown in FIG.3 (d) is a form especially useful when using a GPS receiver with a car navigation apparatus etc. FIG. In general, a car navigation apparatus has a function of reading out map information from a medium such as a CDROM or DVDROM and using it for screen display and the like, and also has a connection interface with a GPS receiver. The present invention can be implemented in such a manner that information such as the number of laps is written in the information storage medium and read out and taken into the position calculation unit 22. In that case, the addition of a circuit / device is not necessary.
[0022]
The third detection principle is to store the reception history of WN information in the past and determine the number of laps of WN information based on the history. As shown in FIG. 3 (e), the lap number detection unit 24 based on this detection principle can be realized by the WN history storage unit 24f and the lap number determination unit 24g. The WN history storage unit 24 f stores the WN information obtained by the navigation data demodulation unit 14. The lap number determination unit 24g determines the current lap number based on the WN information reception history stored by the WN history storage unit 24f and the output of the clock 12 backed up by a battery (not shown), that is, the current time. The position calculator 22 determines the current date and time based on the result.
[0023]
The fourth detection principle is to obtain the current number of laps based on the leap second information value transmitted from the GPS satellite as part of the time information. As shown in FIG. 3 (f), the circulation number detection unit 24 based on this detection principle can be realized by a leap second information extraction unit 24h and a circulation number determination unit 24i. The leap second information extraction unit 24 h extracts leap second information from the output of the navigation data demodulation unit 14. The atomic clock that engraves the GPS system clock has an error with respect to the universal time (UTC), which is determined exclusively based on the rotation of the earth, and as shown in FIG. Accumulate over time. The GPS satellite transmits information such as a Z count in accordance with the GPS system clock, and transmits the accumulated error from January 6, 1980 as leap second information. Since the leap second information increase rate is substantially constant, the number of laps of the WN information can be known by determining the threshold value of the leap second information by the lap number detection unit 24h. In implementing this detection principle, only software changes are required.
[0024]
Even when the present invention is implemented according to any of the four types of detection principles described above, it is possible to search for a GPS satellite and perform positioning, and to reduce the burden on the connection destination device. As described above, conventionally, the circuit or logic in the GPS receiver has been designed so as to give a specific date and time when the WN information becomes zero. For this reason, the year and month for one round of WN is the limit for maintaining a normal output value of date and time. On the other hand, in each of the above-described embodiments, the correct date and time can be obtained by referring to the number of laps of the WN information regardless of the value of the WN information.
[0025]
That is, according to each embodiment of the present invention, since the position calculator 22 determines the time based on the time derived from the WN information and the Z count and the detected number of laps, the position calculator 22 It does not occur that the information regarding the date and time among the information obtained by the above method exhibits a large error due to the circulation of the WN information. Therefore, the process of calibrating the clock 12 based on the incorrect date and time derived without considering the number of laps (the process of adjusting the clock 12 to the incorrect date and time) is not performed, and the signal from the selected GPS satellite cannot be captured. Is less likely to occur. Furthermore, since the date and time obtained from the position calculation unit 22 is accurate even after 19.7 years from the start of manufacture or use, the date and time output based on the output of the position calculation unit 22 is performed at the connection destination device, for example, a car navigation device. This reduces the burden on the connection destination device. Furthermore, each form shown in FIG. 3 can be easily realized.
[0026]
[Addendum]
The present invention can also be expressed in the form of a GPS receiver, its date / time specifying program, a positioning method, a program, or the like.
[0027]
First, the present invention includes WN information that is incremented each time the week changes and is reset to an initial value when a predetermined upper limit value is reached, a Z count that gives a time within the week, and orbit information indicating the orbit of a GPS satellite. Measured by means of receiving from the GPS satellite, means for determining the current week based on the WN information, means for specifying the transmission time of the positioning signal based on the received Z count, and the specified transmission time and the built-in clock Means for obtaining a pseudo distance to a source GPS satellite based on the received time of the positioning signal, and means for collecting pseudo distance and orbit information for a predetermined number or more of GPS satellites and calculating a current position based on the pseudo distance and orbit information. The GPS receiver includes a lap number detecting means for detecting the number of times the WN information circulates in the range from a predetermined point in time in the past to the present. And obtains the current week based on the number of turns and received WN information was.
[0028]
The date and time specifying program according to the present invention increments the WN information that is incremented each time the week changes and is reset to the initial value when the predetermined upper limit value is reached, and the Z count that gives the time within the week from the GPS satellite. A step of receiving as a part, a step of detecting the number of times the WN information has circulated in the range from a predetermined point in the past to the present, and a step of specifying a transmission time of the positioning signal based on the obtained week and the received Z count It is characterized by having.
[0029]
The positioning method and program according to the present invention include a step of receiving orbit information indicating the orbit of the GPS satellite from the GPS satellite, a step of executing the date and time specifying method or program according to the present invention, and the specified transmission time and built-in The step of obtaining the pseudorange to the source GPS satellite based on the reception time of the positioning signal timed by the clock is repeatedly or concurrently executed for a predetermined number of GPS satellites, and the current position is determined based on the result. It is characterized by calculating.
[0030]
In any case, preferably, (1) manually setting the number of laps of WN information from a predetermined point in the past to the present, (2) receiving the laps of WN information from a predetermined point in the past to the present from the outside, ( 3) WN information received from a GPS satellite is stored as a part of the reception history, and the number of laps of WN information from a predetermined past time to the present is calculated based on the stored reception history. (4) Past predetermined time A method such as calculating leap seconds of WN information from a predetermined point in the past to the present based on leap second information received from GPS satellites and receiving leap second information indicating accumulated errors occurring in the GPS system clock from the present to the present It is desirable to detect the number of laps.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a GPS receiver according to an embodiment of the present invention.
FIGS. 2A and 2B are diagrams showing the circulation of WN information, FIG. 2B showing the increase in leap second information value, and FIG. 2C showing the number of circulations of WN information, respectively, with the year on the horizontal axis.
FIGS. 3A and 3B are diagrams showing various forms of a lap number detection unit in the present embodiment, wherein FIG. 3A is a form using hardware switches, FIG. 3B is a form using terrestrial radio, and FIG. FIG. 4 is a diagram showing a form by connection, (d) a form by reading from a medium, (e) a form using a reception history, and (f) a form using leap second information.
[Explanation of symbols]
10 reception control calculation unit, 14 navigation data demodulation unit, 16 reception unit, 20 pseudo distance measurement unit, 22 position calculation unit, 24 lap number detection unit, 24a hardware switch, 24c reception unit, 24d demodulation unit, 24e interface, 24fWN history storage unit, 24g, 24i lap count determination unit, 24h leap second information extraction unit.

Claims (3)

A method used when a GPS receiver is used together with a car navigation device using a map information storage medium in which the number of laps of WN information is stored,
Receiving from a GPS satellite as part of a positioning signal WN information that is incremented each time the week changes and is reset to an initial value when a predetermined upper limit is reached, and a Z count that gives the time within the week;
Detecting the number of times the WN information has circulated in the range from a predetermined point in the past to the present by reading the number of laps of the WN information from the map information storage medium;
Identifying the transmission time of the positioning signal based on the detected number of laps of the WN information and the received WN information and the Z count;
A date and time identification method characterized by comprising: A GPS receiver for use with a car navigation device using a map information storage medium in which the number of laps of WN information is stored,
WN information that is incremented each time the week changes and is reset to the initial value when a predetermined upper limit value is reached, Z count that gives the time within the week, and orbit information indicating the orbit of the GPS satellite are received from the GPS satellite Means,
Means for determining the current week based on the WN information, and specifying the transmission time of the positioning signal based on the determined week and the received Z count;
Means for obtaining a pseudo-range to the source GPS satellite based on the identified transmission time and the reception time of the positioning signal measured by the built-in clock;
Means for collecting pseudorange and orbit information for a predetermined number or more of GPS satellites and calculating the current position based thereon;
Means for detecting the number of times the WN information has circulated in the range from a predetermined point in the past to the present by reading the number of laps of the WN information from the map information storage medium;
Means for determining the current week based on the number of laps of the detected WN information and the received WN information;
A GPS receiver comprising: WN information that is incremented each time the week changes and is reset to the initial value when a predetermined upper limit value is reached, Z count that gives the time within the week, and orbit information indicating the orbit of the GPS satellite are received from the GPS satellite Means,
Means for determining the current week based on the WN information, and specifying the transmission time of the positioning signal based on the determined week and the received Z count;
Means for obtaining a pseudo-range to the source GPS satellite based on the identified transmission time and the reception time of the positioning signal timed by the built-in clock;
Means for collecting pseudorange and orbit information for a predetermined number or more of GPS satellites and calculating the current position based thereon;
Receive leap second information indicating the accumulated error that occurred in the GPS system clock from a predetermined point in the past to the present from the GPS satellite, and calculate the number of laps of WN information from the past predetermined point to the present based on the received leap second information Means for detecting the number of times the WN information has circulated in the range from a predetermined point in the past to the present,
Means for determining the current week based on the number of laps of the detected WN information and the received WN information;
A GPS receiver comprising:

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